In the manufacture of integrated circuits, copper interconnects are generally formed on a semiconductor substrate using a copper dual damascene process. Such a process begins with a trench being etched into a dielectric layer and filled with a barrier layer, an adhesion layer, and a seed layer. A physical vapor deposition (PVD) process, such as a sputtering process, or an atomic layer deposition (ALD) process, may be used to deposit a tantalum nitride (TaN) barrier layer and a tantalum (Ta) or ruthenium (Ru) adhesion layer (i.e., a TaN/Ta or TaN/Ru stack) into the trench. The TaN barrier layer prevents copper from diffusing into the underlying dielectric layer. The Ta or Ru adhesion layer is required because the subsequently deposited metals do not readily adhere to the TaN barrier layer. This may be followed by a PVD sputter process to deposit a copper seed layer into the trench. An electroplating process is then used to fill the trench with copper metal to form the interconnect.
As device dimensions scale down, the aspect ratio of the trench becomes more aggressive as the trench becomes narrower. This gives rise to issues such as trench overhang during the copper seed PVD deposition, leading to pinched-off trench openings and inadequate gapfill. Additionally, as trenches decrease in size, the ratio of barrier metal to copper metal in the overall interconnect structure increases, thereby increasing the electrical line resistivity and RC delay of the interconnect.
In addition to the above, seed integration issues are observed at the 32 nanometers (nm) and below nodes using conventional seed/barrier processes. With respect to manufacturing, use of separate barrier and seed layers makes tooling expensive thereby increasing the overall price of production.
The TaN barrier layer may be deposited by ALD using amine-containing tantalum precursors and ammonia gas (NH3). Unreacted ammonia can cause photoresist “poisoning” in subsequent fabrication operations.
Recently, low thermal stability ruthenium precursors have been used to deposit ruthenium films in seed/barrier applications in an attempt to address the problems discussed above. Typically, the ruthenium precursor is deposited in the presence of molecular oxygen using ALD. In one example, the precursor Ru3CO12 was used to deposit a ruthenium-containing layer, resulting in layers with high carbon and oxygen contamination.